Method of eliminating carbon from and controlling the temperature of molten steel



March 28, 1950 P. M. HULME 2,502,259

METHOD OF ELIMINATING CARBON FROM AND CONTROLLING TEE TEMPERATURE OF MOLTEN STEEL Filed Dec. 12, 1946- INVENTOR 74,5} M Va/me w E ATTORNEY Patented Mar. 28 1950 METHOD OF ELIMINATING CARBON FROM AND CONTRQLLING THE TEMPERATURE OF MOLTEN STEEL Philip M. Hulme, Stamford," -Conn., assignor 'to Air Reduction Company, Incorporated. New U York, N. Y., a ccrporationrol New York Application December 12, 1946, Serial No. 715,721

4 Claims.

' This invention relates to decarburization of steel and particularly to an improved procedure for the oxidationof carbon in molten steel to bring the carbon-content to a-satisfactory low point.

In'lowering the carbon content of molten steel, it has been the practice heretofore to add iron ore-to the-furnacefor reaction with the carbon of the steel. The reaction is, however, relatively slow, and it is not readily controllable. The procedure has persisted in common practice merely because no better method has been available.

It is the object of the present invention to provide a rapid-"effective and economical method of oxidizing carbon in molten steel which involves simultaneously controlling the temperature of the molten steel.

Another object of the invention is the provision of a method of reducing the carbon content of molten steel which is readily controllable and hence adapted to produce the desired effect in the minimum time and with facility heretofore impossible to attain.

Other objects and advantages ofthe invention will be apparent as it is better understood by reference to the following specification and accompanying drawing, which illustrates diagrammatically an apparatus suitable for the practice of the invention.

While the invention is described in connection withanelectricfurnace'operation, it may be carried out in the open hearth or other suitable steel producing furnace. The procedure and the apparatus required are relatively inexpensive.

The invention depends upon the introduction of iron oxide, preferably in the form of finely divided crushed iron ore, in a stream of an oxidiz-' ing carrier gas containing more than 45% of oxygen beneath the surface of the molten metal and adjusting, as required, the proportions of the iron oxide and the amount of oxygen introduced by the carrier gas to either maintain a desired temperature of the molten metal or else to raise the temperature of the molten metal. The gaseous carrier may be oxygen of commercial purity, i. e., 99.5% or better, or of a lower grade, ranging from 45% to 99.5% purity.- In either case, the gas should be dry to avoid introduction of hydrogen to the metal.

In carrying out the invention, the iron oxide is delivered to the stream of oxidizing carrier gas and thence conveyed to a point beneath the surface of the molten metal in which it is rapidly disseminated. Oxidation of the carbon occurs in accordance with the followin reaction:

2 The formation of carbon monoxide is aided by the presence--of-bubbles of the carrier gas in the molten steel; Thus, the reaction is facilitated and proceeds much more rapidly and is more readily controllable than'int-he-case of themere addition of ironore to the furnace. The reaction does not in'fact-take place'effectively unless an interfacesuchas that provided'by a gas bubble ispresent. I

The reaction between iron oxide and "carbon isendothermic. Hence, the use of an oxidizing carrier gas of high oxygen contentprovides an effective means for maintaining theheat balance. For example, one gross ton of molten steel containing .75% carbon requires 73.4' pounds of F6203 to oxidize the carbon. Since the ore'is introduced cold, the net effect of the reaction is to reduce the bath temperature 314 F. If .'75% carbon is burned with oxygen, an increase in metal temperature of 192 F. is noted. Thus, by using 5.5 to 6.6 cubic feet of oxygen per pound of Fezoalthe bathtemperature may be maintained substantially constant and by varying this ratio the temperature may be raised orlowered. There is a further advantage in the use of oxygen as the carrier gas, since the oxygen itself consumes some of the. carbon in the steel. I Referring to the drawings, 5 indicates the foundation of an electric furnace 6 provided with the-usualelectrodes I. The molten bath f steel is maintained within the furnace 5, which has an opening 9 in the Wall thereof.

In order to introduce iron oxide to the molten metal, I provide a source of gas under pressure such as a trailer It) carrying cylinders II which are connected to a manifold I2 through which the gas is withdrawn. A pressure regulating valve I3 permits reduction of the initial pressure of the gas in the cylinders II to the pressure desired in the pipe I4 which is connected to a housing I5 including an injector nozzle I6.

The iron oxide to be supplied is maintained within an air-tight receptacle I'l connected by a pipe I8 having a control valve I9 to the housing I5. Gas under pressure, preferably the same gas supplied from the cylinders I I, is maintained in the cylinder I8 having an outlet I9 with a pressure regulating valve 26 which reduces the pressure to that desired in the pipe 2| connected to the removable closure 22 of the receptacle I'I. Thus, suitable gas pressure may be maintained above the iron oxide 23 in the receptacle I1, serving to move it steadily to the housing I5.

As the result of the injector action, the iron oxide is picked up and carried through the pipe 24 to a metal pipe 25 which is adapted to be thrust beneath the surface of the molten metal bath 8. A by-pass 26, controlled by a valve 21 permits the passage of additional gas to the pipe 24 without passing through the housing l5, so that the flow of gas may be regulated in the desired proportion. Thus, the iron oxide from the receptacle l! is fed at the desired rate directly to the molten metal bath 8 for reaction with the carbon therein.

The pipe 25 may be of steel or iron. Where oxygen of commercial or higher purity is used as the carrier gas, it is desirable to maintain a velocity of flow which is sufiicient to maintain the lower end of the pipe 25 at a temperature below that of ignition of the metal with oxygen. This can be accomplished readily. If desired, the pipe 25 may be coated with an insulating material such as sillimanite (a form of alumina) or other suitable refractory material, to assist in protecting the pipe from oxidation. The lower end of the pipe will gradually melt and hence the pipe must be advanced as the operation continues. Howevenexperience has demonstrated that consumption of the pipe by melting is relatively low, and a new pipe may be substituted as required as the operation continues.

It is essential that the carrier gas be thoroughly dried to avoid the formation of hydrogen and contamination of the steel therewith.

The procedure as described materially reduces the time required for decarburizing steel, since dissemination of the iron oxide through the metal results in a relatively rapid reaction and the loss of heat and the loss of time necessary to bring the metal to the required temperature is avoided. The reaction is moreover accelerated by the provision of a multiplicity of interfaces resulting from the bubbling of the carrier gas through the molten metal.

Various changes may be made in the procedure asdescribed and in the form of apparatus employed without departing from the invention or sacrificing the advantages thereof.

j I claim:

1. The method of modifying the carbon content of molten steel and simultaneously controlling the temperature thereof which comprises introducing finely-divided iron oxide suspended in a stream of an oxidizing carrier gas containing more than 45% of oxygen beneath the surface of the molten metal, and adjusting, as required, the proportions of the iron oxide and the amount of oxygen introduced by the carrier gas to obtain a desired temperature of the molten metal.

2. The method of modifying the carbon content of molten steel as set forth in claim 1 in which the proportions of iron oxide and the amount of oxygen introduced by the carrier gas are adjusted to maintain a desired temperature of the molten metal.

3, The method of modifying the carbon content of molten steel as set forth in claim 1 in which the proportions of iron oxide and the amount of oxygen introduced by the carrier gas are adjusted to raise the temperature of the molten steel.

4. The method of modifying the carbon content of molten steel and simultaneously controlling the temperature thereof which comprises introducing finely-divided iron oxide suspended in a stream of an oxidizing carrier gas containing about 99.5% of oxygen beneath the surface of the molten metal, and adjusting, as required, the relative proportions of the iron oxide and oxygen introduced to obtain a desired temperature of the molten metal.

PHILIP M. HULME.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 193,551 Reese July 24, 1877 987,704 Deemer Mar. 28, 1911 1,484,465 Billings Feb. 19, 1924 1,505,281 Nagelvoort Aug. 19, 1924 1,709,389 Davis Apr. 16, 1929 1,809,436 Carman June 9, 1931 1,949,731 Soldatofi Mar. 6, 1934 1,968,917 Soldatoff Aug. 7, 1934 2,077,568 Kinzel Apr. 20, 1937 FOREIGN PATENTS Number Country Date 2,243 Great Britain of 1879 457,645 France Sept. 22, 1913 252,267 Italy Mar. 7, 1927 

1. THE METHOD OF MODIFYING THE CARBON CONTENT OF MOLTEN STEEL AND SIMULTANEOUSLY CONTROLLING THE TEMPERATURE THEREOF WHICH COMPRISES INTRODUCING FINELY-DIVIDED IRON OXIDE SUSPENDED IN A STREAM OF AN OXIDIZING CARRIER GAS CONTAINING MORE THAN 45% OF OXYGEN BENEATH THE SURFACE OF THE MOLTEN METAL, AND ADDUSTING, AS REQUIRED, THE PROPORTIONS OF THE IRON OXIDE AND THE AMOUNT OF OXYGEN INTRODUCED BY THE CCARRIER GAS TO OBTAIN A DESIRED TEMPERATURE OF THE MOLTEN METAL. 